.overlay button {
  background: #3498db;
  background-image: -webkit-linear-gradient(top, #3498db, #2980b9);
  background-image: -moz-linear-gradient(top, #3498db, #2980b9);
  background-image: -ms-linear-gradient(top, #3498db, #2980b9);
  background-image: -o-linear-gradient(top, #3498db, #2980b9);
  background-image: linear-gradient(to bottom, #3498db, #2980b9);
  -webkit-border-radius: 28;
  -moz-border-radius: 28;
  border-radius: 28px;
  border: 0;
  font-family: Courier New;
  color: #ffffff;
  font-size: 20px;
  padding: 10px 20px 10px 20px;
  text-decoration: none;
  margin-top: 200px;
}

.overlay {
  width: 100%;
  height: 100%;
  display: table;
  background: rgba(0, 0, 0, 0.85); 
  z-index: 1000;
  position: absolute;
  top: 0;
  left: 0;
  text-align: center;
}